1. Field of the Invention
The present invention relates to a plasma tube array-type display device joining a plurality of plasma tube array-type display sub-modules to each other comprising a plasma tube array in which a plurality of plasma tubes is arranged in parallel, and a luminance correcting method. More particularly, the present invention relates to a plasma tube array-type display device and a luminance correcting method capable of reducing variations in luminance values of a plasma tube array.
2. Description of the Related Art
As a technology for realizing a next-generation large-screen display device, a plasma tube array-type display sub-module has been developed with a structure that a plurality of plasma tubes each filled with a discharge gas is arranged in parallel. For example, a large-screen display device having a scale of several meters by several meters in size can be constructed of a plasma tube array-type display system module that a plurality of plasma tube array-type display sub-modules of one square-meter in size is joined to one another. The display device of this type does not need either a large glass substrate to be handled, like an LCD, a PDP and the like, nor a large-scale facility and achieves even image quality at low cost.
Typically, a large-screen plasma tube array-type display device can be constructed as follows. That is, a plasma tube array-type display sub-module is prepared in such a manner that a plasma tube array is integrated with a structural body called a sub-module frame of a certain size. Then, the plurality of plasma tube array-type display sub-modules is joined to one another. Herein, the “plasma tube array-type display sub-module” refers to a display film component as described above which includes a plasma tube, that is, a semi-finished product of a display panel which does not have a drive circuit, a power supply circuit and the like incorporated. FIGS. 1A and 1B are perspective views schematically showing a configuration of a plasma tube array of a conventional plasma tube array-type display sub-module. FIG. 1A is a perspective view schematically showing a configuration of a plasma tube array of a plasma tube array-type display sub-module, and FIG. 1B is a perspective view partly showing the configuration of the plasma tube array of the plasma tube array-type display sub-module.
As shown in FIG. 1A, the conventional plasma tube array-type display sub-module has a rectangular shape as it comprises a part of a rectangular screen and a plurality of plasma tubes 131, 131, . . . each filled with a discharge gas is arranged in parallel. The plasma tube array-type display sub-module is constructed in such a manner that the plurality of plasma tubes 131, 131, . . . arranged in parallel is held between an address electrode sheet 133 with a plurality of address electrodes 132, 132, . . . formed thereon along the longitudinal direction of the plasma tubes 131, 131, . . . and a display electrode sheet 135 with a plurality of display electrode pairs 134, 134, . . . formed thereon substantially orthogonal to the longitudinal direction of the plasma tubes 131, 131, . . . .
The plurality of display electrode pairs 134, 134, . . . are formed in stripes on the display side of the plasma tube array-type display sub-module orthogonal to the longitudinal direction of the plasma tubes 131, 131, . . . . Herein, the display electrode pair 134 is not particularly limited as long as display discharge can occur inside the plurality of plasma tubes 131, 131, . . . located between the adjacent display electrode pairs 134, 134. The address electrodes 132, 132, . . . are formed on the back side of the plasma tube array-type display sub-module for each plasma tube 131 along the longitudinal direction of the plasma tubes 131, 131, . . . . Herein, the address electrode 132 is not particularly limited as long as an emit light cell is formed at an intersection of the address electrode 132 and the display electrode pair 134, 134.
As described above, as shown in FIG. 1B, the plasma tube array-type display sub-module achieves color display in such a manner that each plasma tube 131 comprises a single-color phosphor layer 136. Examples of the phosphor layer 136 comprise a red (R) phosphor layer 136R, a green (G) phosphor layer 136G and a blue (B) phosphor layer 136B. A set of the plasma tube 131 comprising the R phosphor layer 136R, the plasma tube 131 comprising the G phosphor layer 136G and the plasma layer 131 comprising the B phosphor layer 136B forms one pixel, so that the plasma tube array-type display sub-module can achieve color display.
Because of the structure of the plasma tube 131, it is difficult to manufacture the plasma tubes 131, 131, . . . for each color so that the luminance of all of the plurality of plasma tubes 131, 131, . . . is completely even. When all of structural elements such as shape and thickness of glass tubes, as well as the shape, thickness, and the like of the phosphor layers are made even, the luminance is even. However, it is unrealistic to manufacture the plasma tubes without any error in the elements as the cost increases because of a decrease in conforming item ratio, an increase in manufacturing steps, and the like. In the case of configuring as a plasma tube array-type display sub-module, luminance differences occur in each plasma tube 131 of the same color, for example, for red (R), and it causes variations in luminance in the direction where the plasma tubes 131, 131, . . . are arranged in parallel. Due to occurrence of the luminance differences in each plasma tube 131 of the same color, the color balance varies among pixels each constructed by a set of plasma tubes 131, 131, 131 for three colors of R, G, B, and it is perceived as variations in colors (color unevenness) in the direction in which the plurality of plasma tubes 131, 131, . . . is arranged in parallel.
In the longitudinal direction of the plasma tubes 131, 131, . . . the luminance difference between the adjacent emit light cells is small. For example, the gradient of a luminance value which gradually increases is shown. Here, “luminance value” means the brightness level of each discharge cell when the same driving voltage is applied between the display electrodes forming a plurality of discharge cells. The reason is considered that, in the process of manufacturing the plasma tube 131, since the plasma tube 131 is particularly long, at the time of being evacuated and filled with a gas, the state (cleanness or the like) of the internal discharge surface of the plasma tube 131 varies according to the distance from the evacuating port. Therefore, comparing to the longitudinal direction of the plasma tubes 131, 131, . . . , in the parallel direction in which the plurality of plasma tubes 131, 131, . . . is arranged in parallel, the luminance difference between the adjacent emit light cells is larger, and the gradient of the luminance value indicative shows a sharp luminance change. There is, consequently, a problem such that the luminance variations are more easily perceived in the parallel direction.
To correct variations in light emission luminance of a display element, for example, in JP 11-344949 A, correction data for correcting variations in the light emission luminance of each display element is stored in a memory device and, at the time of driving the display element, the correction data is supplied to the corresponding driver. In a state where variations in the light emission luminance are corrected, display can be driven.
For example, in JP 2004-86165 A, a uniform image is displayed on a display device, luminance of each display element is detected, and a luminance target value of each display elements is calculated. On the basis of the luminance target value of each display element, a luminance correction coefficient on each display element is calculated. In such a manner, in the case of configuring a large-screen display device by arranging a number of display units, variations in luminance values of each display unit and joining portions are inconspicuous, and the image quality is improved.
In both of JP 11-344949 A and JP 2004-86165 A, however, luminance data of all the display elements is detected and, on the basis of each luminance data, correction data for correcting luminance of each display element is provided for each display element. Therefore, particularly for a high-definition image or the like, it is necessary to store a considerable amount of correction data and perform process with the correction data. The high-definition image is displayed by 1920×1080=2073600 pixels. In the case where each pixel has, for example, 64 levels of luminance difference information, the total pixels of the three colors of R, G, B is 2073600×3 (sub-pixels)×6 (bits) (64 levels)=37324800 (bits)=4665600 (bytes), that is an information amount of about 4.6 Mbytes. In the case of 60 Hz television frame, the information amount of about 280 Mbytes has to be processed per second, which is calculated by 4665600 (bytes)×60 (Hz)=279936000 (bytes), and for which large-amount memory and a high-speed computing circuit are required.